In an aspect of conventional packaging technologies, such as wafer level packaging (WLP), redistribution layers (RDLs) may be formed over a die and electrically connected to active devices in a die. External input/output (I/O) pads such as solder balls on under-bump metallurgy (UBMs) may then be formed to electrically connect to the die through the RDLs. An advantageous feature of this packaging technology is the possibility of forming fan-out packages. Thus, the I/O pads on a die can be redistributed to a greater area than the die, and hence the number of I/O pads packed on the surfaces of the dies can be increased.
In such packaging technologies, RDLs typically include one or more polymer layers formed over the die and molding compound. Conductive features (e.g., conductive lines and/or vias) are formed in the polymer layers and electrically connect I/O pads on the die to the external connectors over the RDLs.